The benefits of recycling materials are well known. Most common household materials, including paper, metals and glass, can be recycled for re-use by industry. However, the cost of recycling varies depending upon the material.
Recycling of glass in particular has been a costly process. The main reason is that industries which use recycled glass require that the glass be largely contaminant free. Household waste recycling programs generally do not discriminate between glass and ceramic recyclables, or between glasses of different colours. As such, glass recyclables collected by recycling authorities tend to be a mixture of different colours of glasses and ceramics, as well as contaminants such as foil or paper labels and any non-recyclable refuse that finds its way into a bottle or jar or other refuse in a recycling bin.
These contaminants present a problem in conventional recycling processes. Prior to the invention there has not been a satisfactory method available for eliminating contaminants such as small paper and foil particles and chemical adhesives from the recycled glass. These contaminants render the recycled glass unsuitable for use in many industrial processes.
Moreover, the ceramic content of the mixture presents a particular problem, because ceramic does not burn off at temperatures which will eliminate most other contaminants and it is often difficult to physically distinguish ceramic from glass so it is virtually impossible to eliminate the ceramic content of the mixture prior to processing. However, recycled glass with any significant content of large ceramic particles is useless to many industries, for example bottle production, because these particles weaken the structure of the recycled product.
As such, existing recycling programs cannot recover much of the glass which is collected for recycling and end up disposing of it in landfill sites with other non-recoverable refuse.
The present invention provides a system and method for recycling glass from a three-mix cullet which includes whole and broken glass recyclables of any colour as well as ceramics and other contaminants. The system and method of the invention requires minimal preliminary separation of materials, saving time and labour costs. The recycled glass cullet is over 99% contaminant free, which is acceptable for use in most industries, and can be produced in a powder form particularly suitable for producing glass fiber insulation, sand blasting slurries, water filtrates, glass beads for reflective paint and many other uses. The recycled glass is also environmentally safe and does not cause silicosis, even in powder form.
The invention accomplishes this by crushing the three mix cullet to a size at which the glass and ceramic can be separated from metal, plastic and other contaminants, washing the resulting mixture in a rotary drum apparatus to remove adhesives and other buoyant or "floatable" contaminants, heating the washed mixture to eliminate any remaining combustibles and reduce moisture content, and optionally further crushing the glass particles to a particle size of minus 12 mesh.
It has been found that ceramics when reduced to a particle size of less than 20 mesh do not adversely affect recycled glass. Ceramic particles of this size dissipate in industrial furnaces and do not form part of the recycled product. Thus, it becomes unnecessary to eliminate ceramics from the recycling mixture, so long as they are crushed to the required size so that they no longer form contaminants in the recycled product. By virtually eliminating contaminants such as paper, foil, ferrous and non-ferrous metals and chemical adhesives, recycled glass produced by the invention is suitable for reuse in most industrial applications which would otherwise be unable to use recycled glass.
The invention further provides a novel glass washing apparatus, comprising a rotating drum having vanes disposed along its interior wall. The drum is composed of sections, each section being supported by rollers and being differentially rotated by a drive mechanism to reduce wear caused by misalignment of the drum on the rollers. As the drum rotates the glass slurry is tossed forwardly by the vanes, and progressively conveyed toward the discharge outlet. The abrasion of the glass particles against the vanes and against neighbouring particles in the presence of the wash solution removes any adhering buoyant contaminants.
The present invention thus provides a system for recycling a waste glass cullet, comprising a first screening station for separating large glass shards of approximately one inch in diameter from smaller glass shards in the cullet, a crusher to reduce the large glass shards to smaller glass shards smaller than approximately one inch in diameter, a second screening station to separate remaining large contaminants having a diameter of approximately one inch or greater from the cullet, a presoak holding tank partially filled with a presoaking solution, a rotary washing apparatus comprising a drum having a vane disposed along an inner wali of the drum to toss the cullet in a washing solution, the vane being oriented so that the cullet is tossed progressively forwardly toward a discharge outlet of the drum, to remove buoyant contaminants from the cullet, a dewatering apparatus to remove excess water from the cullet, and a dryer for reducing the moisture content of the cullet.
The present invention further provides method of recycling a waste glass cullet, comprising the steps of separating large glass shards of approximately one inch in diameter from smaller glass shards in the cullet, crushing the large glass shards to smaller glass shards smaller than approximately one inch in diameter, separating large contaminants having a diameter of approximately one inch or greater from the cullet, presoaking the cullet in a presoaking solution, washing the cullet in a rotary washing apparatus comprising a drum with a vane disposed along an inner wall of the drum to toss the cullet in a washing solution, the vane being oriented so that the cullet is tossed progressively forwardly toward a discharge outlet of the drum, to remove buoyant contaminants from the cullet, dewatering the cullet to remove excess water, and reducing the moisture content of the cullet.
The present invention further provides a rotary drum washer for removing buoyant contaminants from glass cullet, comprising a rotating drum having a helical vane disposed along an inner wall of the drum and one or more radially oriented paddles disposed along an inner wall of the drum to toss the cullet in a washing solution, the vane being oriented so that the cullet is tossed progressively forwardly toward a discharge outlet of the drum.